1. Field of the Invention
The present invention is directed to a fixing station for fixing toner images on a carrier material, having a heating device with at least one radiant heat source that emits radiation in the direction of the carrier material, and having a cover device with which an undesired incidence of radiation onto the carrier material can be prevented.
2. Description of the Related Art
In electrographic printers or copiers, the toner image transferred from an intermediate carrier, generally a photoconductor, onto the carrier material, generally paper, must be fixed, i.e. it must be joined so as to be smear-proof and abrasion-proof to the carrier material. Heat/pressure fixing is currently usually utilized in electrophotography. When no pre-heating, for example with the assistance of a heating saddle, of the carrier material is undertaken, this is usually limited to approximately 0.5 m/s through 0.7 m/s in terms of processing speed. In the duplex printing mode wherein the front side and the back side of a carrier material are printed, the fixing process is relatively difficult because both sides are still covered with smearable toner images. A high fixing quality given simultaneous fixing of the front side and of the back side of the carrier material can only be achieved with relatively soft fixing drums, for example silicone drums. These fixing drums have a low service life and are uneconomical. Such soft fixing drums are therefore only utilized given printers having a relative low printing volume. Since soft fixing drums are utilized at both sides of the carrier material, the guidance of the carrier material becomes problematical. Such fixing drums are therefore not suited in the further-processing of continuous form paper.
For said reasons, it is desirable to fix toner images contact-free, whereby a relatively broad spectrum of carrier material can be utilized. Another goal of contact-free fixing is comprised in achieving a high fixing quality without smearing effects.
A contact-free fixing method is known wherein the toner material is softened with the assistance of a solvent material, so that it unites better with the fibers of the carrier material. When, however, chromatic toner is employed, it can occur that the color pigments are dissolved to different extents, which can potentially lead to a color-dependent smearing of the toner images. Moreover, the known environmental problems given the utilization of solvents arise.
Another known fixing method that works contact-free is what is referred to as photoflash fixing, whereby the toner is fixed on the carrier material with the assistance of high-energy light pulses. The wavelength of the radiation usually lies in the visible through ultraviolet range of the spectrum. Since the various color toners absorb to different extents in this wavelength range, a photoflash fixing is not suitable for multi-color printing.
Another fixing station is disclosed by European Patent Document EP-A-0 629 930. The fixing station is employed for an electrostatic printer in order to fix toner material on paper. The cover device serves the purpose of preventing the incidence of radiation during a heating-up phase or during a standstill of the carrier material. In the closed condition of the cover device, the active surfaces of the radiant heat source emitting thermal radiation face away from the carrier material. In this condition, the cover device surrounds the radiant heat source, so that the heating-up phase is shortened. During normal operation wherein the toner material is fixed on the carrier material as a consequence of the incident radiant heat, the radiant heat source faces toward the carrier material and the radiation can impinge the carrier material unimpeded.
Japanese Patent Document JP-A-62-055685 discloses a fixing device wherein a cover device can be moved into the beam path between a radiant heat source and a carrier material. The cover device comprises a plate of heat-resistant material. The cover device is removed from the beam path in the normal operating condition. Given an abnormal operating condition, the cover plate is shoved between the carrier material and radiant heat source.
The Japanese Patent document JP-A-60-014268 is directed to a fixing device wherein a cover plate can be moved into the beam path between a radiant heat source and a carrier material. The intensity of the fixing is set with the assistance of this cover plate dependent on the paper thickness of the carrier material. A detector thereby determines the paper thickness, whereupon the cover plate is swivelled. The fixing device can be set to different paper thicknesses relatively fast in this way.
An object of the invention is to provide a fixing station that works with high processing speed and assures a high print quality.
This object is achieved by a fixing station for fixing toner images on a carrier material, including a heating device with at least one radiant heat source that emits radiation in the direction of the carrier material, and having a cover device movable essentially parallel to the moving direction of the carrier material and that can be moved in to the beam path between radiant heat source and carrier material, in that, given a stop of the carrier material, the cover device is moved with the velocity VR, according to the relationship: VR=xe2x88x92VP, wherein vp is the transport velocity of the carrier material; and in that, given continued transport of the carrier material with the velocity VP, the cover device is moved with the velocity VR, according to the relationship: VR=VP. Advantageous developments provided by the cover device having at least the width of the carrier material. Specifically, the cover device is flexible as viewed in moving direction of the carrier material. In one embodiment, the cover device contains a band. Alternately, the cover device contains a plurality of strip-shaped lamellae that form a window blind, whereby adjoining lamellae preferably overlap. The band or, respectively, the lamellae can be wound up in the fashion of a winding.
In a preferred embodiment, an endless deflection means is arranged around the heating device; and the band or, respectively, the window blind can be moved along the deflection device. The deflection device may contain a tensing mechanism that keeps the band or, respectively, the window blind in a tensed condition. A feature of the invention provides that the cover device has a length that is adequate in order to cover the entire radiation of the radiant heat source in the direction of the carrier material. The cover device may contain a rigid plate for covering the radiation.
The fixing station of one embodiment has a radiant heat source with a radiation temperature in the range from 500xc2x0 C. through 800xc2x0 C. and the maximum intensity of the radiation lies at a wavelength greater than 2 xcexcm. In one embodiment, a respective heating device each having at least one radiant heat source is arranged at both sides of the carrier material, whereby a respective cover device can be moved into the beam path between radiant heat source and carrier material, whereby both cover devices are preferably moved by a common drive. Such a fixing station may be employed for a printer device or copier device that works in duplex printing mode.
A ceramic flat radiator, a crystal radiator or, in particular, a foil radiator can be employed as the radiant heat source. In one aspect of the invention, the radiant heat source is pre-heated. Specifically, the radiant heat source is pre-heated to a temperature above 200xc2x0 C.
Advantages of the invention are realized when a temperature Tm is established in the steady state at the carrier material given an operation of the radiant heat source with nominal power NL; and the radiant heat source is preheated such that a temperature of approximately 0.45 Tm is established on the carrier material. A further feature of the invention is that a temperature sensor acquires the temperature on the carrier material, preferably when it departs the fixing station; and the energy supplied to the radiant heat source is set such that it lies slightly above the fixing temperature Tf. The fixing temperature amounts to, for example, 0.8xc3x97Tm.
A feature of the invention provides that a power control is provided that supplies electrical energy to the radiant heat source; in the operating condition with constant printing, the power control sets a power of approximately 80% NL, whereby NL is the nominal power; in the operating condition with short stoppage of less than 10 seconds, the power is to set to 60% through 80% NL; given an operating condition with long stoppage of  greater than 10 seconds through  less than 5 minutes, a power of 30% through 60% NL is set; in the operating condition of standby mode having a waiting time of  greater than 5 minutes, a power of less than 30% NL is set; and given the start operating condition, a power of 100% NL is set.
Each radiant heat source is divided to a plurality of zones that are respectively separately supplied with the electrical energy; and the zones are supplied with electrical energy dependent on the width of the carrier material. As a preferred development, zones opposite which no carrier material resides are driven with reduced power. In one example, a longitudinal edge of the carrier material lies within a zone. Further, a plurality of zones are combined and driven like a single zone. In embodiments having two heating devices, zones residing opposite one another are driven with the same power. The zones residing opposite one another may be connected in series. As a further aspect, the power control ensues with a pulse packet control or a phase control.
A temperature regulation ensues such that a temperature higher than the fixing temperature is set in zones having carrier material and a lower temperature is set in zones without carrier material. A temperature regulation ensues only in zones with carrier material.
The cover device may be connected to a safety mechanism that contains an energy store; and, given outage of the drive for the cover device, energy is taken from the energy store with which the cover device is moved by the safety mechanism into the beam path between radiation source and carrier material. In an exemplary embodiment, the energy store is a spring energy store that preferably contains a linear spring, a rotatory spring or a gas spring. The energy store is filled with energy given every closing movement of the cover device, or alternately, the energy store is filled once with energy by a drive of the cover device and is subsequently locked by a locking mechanism; and the locking is released given outage of the drive. The locking mechanism may contain an electromagnet that is permeated by current during normal operation; and the lock is released given outage of the current and drop-off of the electromagnet. The drive for the cover device may contain a magnetic coupling that uncouples the drive given outage of the drive.
Shock absorbers that damp the impact of the cover devices are contained in the heating devices.
The traction means is conducted over a deflection roller.
The locking mechanism contains a swivel lever with an oblong hole guide; the retainer magnet holds the swivel lever at its projecting end; a cross pin of the deflection roller is guided in a stationary longitudinal guide and in the oblong hole guide; given a drop-off of the retaining magnet, the swivel lever is turned until oblong hole guide and longitudinal guide are aligned with one another and the cross pin moves in both guides.
According to the invention, the heating device contains a radiant heat source as a result whereof the fixing procedure ensues contact-free. Problems related to the guidance and the pressure charging of fixing drums are thus avoided. The employment of a radiant heat source, however, has the disadvantage that the heating of the cooling of the carrier material involves a relatively high time constant, as a result whereof problems arise when starting printing, given standstill of the carrier material or given intermittent printing. According to the invention, a cover device is proposed that can be moved into the beam path between radiation source and carrier material or given intermittent printing. According to the invention, a cover device is proposed that can be moved into the beam path between radiation source and carrier material. With the assistance of this cover device, defined exposure time for achieving an optimum fixing can be achieved even given frequent starting and stopping of the movement of the carrier material. Due to the contact-free heating of the carrier, a high color reproducibility and uniformity of the fixing of the toner image can be achieved.
The fixing station is preferably employed for a printer device or copier device having high printing performance that works in duplex printing mode, whereby toner images of the front side and of the back side of the carrier material are simultaneously fixed. In this operating mode, heating devices and corresponding cover devices are provided at both sides of the carrier material.